In order to study the influence of pore pressure change caused by unbalanced injection and production in oil and gas reservoirs on geomechanics, the relationship between normal stress and shear stress was analyzed by establishing a geomechanical model of porous reservoir elastic reservoir with closed faults. The influence of pressure changes on the horizontal geostress field near the fault. The results show that the change of pore pressure causes shear stress near the closed fault, and the magnitude and direction of the stress field of the reservoir change. Due to the influence of shear stress, the magnitude of the ground stress decreases linearly. The direction of the geostress also decreases. Deflection may occur. The deflection angle is a function of the pore pressure change value, the angle of the fault, and the Poisson"s ratio of the rock. After considering the dewatering effect and the roof effect, the reservoir pressure change will also have a certain range of influence on the ground stress of the upper cover layer. Taking the 18-1 oilfield in Bohaikou as an example, the influence of reservoir pressure failure on the geostress field of the caprock is estimated to be no more than 20m.